Hydrophilicity gradient in covalent organic frameworks for membrane distillation

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Global freshwater scarcity necessitates advanced desalination technologies.
• Membrane distillation (MD) offers a promising route for water purification using low-grade heat.
• Current MD membranes face limitations in permeance and wetting due to structural control challenges.

Purpose of the Study:

• To engineer a novel membrane distillation membrane with enhanced performance.
• To overcome limitations of existing membranes by introducing precise structural and chemical control.
• To improve water flux and anti-fouling/anti-wetting properties for efficient desalination.

Main Methods:

• Fabrication of covalent organic framework (COF) films with engineered defects.
• Creation of vertically aligned channels with a controlled hydrophilicity gradient by removing imine bonds.
• Integration of the COF membrane onto a supporting layer for desalination testing.

Main Results:

• The developed COF membrane exhibits a hydrophilicity gradient within its channels.
• This gradient enables selective water transport and a precise liquid-vapor phase change interface.
• Achieved a water flux of 600 L m⁻² h⁻¹ at 85°C feed and 16 kPa, nearly tripling state-of-the-art performance, with anti-fouling and anti-wetting capabilities.

Conclusions:

• The engineered COF membrane demonstrates superior performance in membrane distillation for desalination.
• The strategy of defect engineering in COFs provides precise structural and functional control for membrane applications.
• This work paves the way for advanced gradient membranes in molecular sieving and water purification.